A wireless telecommunications system has been proposed with a central terminal, or station, arranged to communicate via wireless links with a plurality of subscriber terminals, or stations, at subscriber locations to implement a wireless telephony system. The system is intended to be used with fixed subscriber locations rather than the more familiar mobile cellular telephone systems.
The system finds a wide variety of possible applications, for example in rural, remote, or sparsely populated areas where the cost of laying permanent wire or optical networks would be too expensive, in heavily built-up areas where conventional wired systems are at full capacity or the cost of laying such systems would involve too much interruption to the existing infrastructure or be too expensive, and so on.
The central terminal is connected to a telephone network and exists to relay messages from subscribers in the cell controlled by the central station to the telephone network, and vice versa. In a typical arrangement, a central terminal may have a plurality of modems for supporting a plurality of wireless links to subscriber terminals. Each subscriber terminal may be able to support more than one line, and so the number of lines supported may be greater than the number of links.
Typically, a plurality of modems at the central terminal may share one connection to the exchange through which all calls to and from subscriber terminals supported by those modems pass. These calls are sent over this single connection in blocks called frames, a frame consisting of a number of timeslots. The exchange will place a call for a particular subscriber terminal on a particular timeslot, so that call information destined for a particular subscriber terminal can be extracted by the central terminal and passed to the appropriate modem for sending over a wireless link to that subscriber terminal. Hence, the central terminal performs fixed timeslot mapping to map calls from particular timeslots in the exchange--central terminal connection to particular wireless links to subscriber terminals, and vice versa, thereby routing calls between the subscriber terminals and the exchange.
Thus, it is apparent that such a central terminal has little flexibility in the way it manages calls. In UK patent application no 9621070.3, a technique for alleviating this problem was disclosed in which the central terminal was provided with a storage containing a phone number list associating phone numbers for the subscriber telecommunications equipment connectable to that central terminal with corresponding lines to subscriber telecommunications equipment.
By that approach, the central terminal was provided with far more flexibility in the way it manages calls, since the central terminal is no longer restricted to performing fixed mapping. By providing a phone number list within the central terminal, associating phone numbers for subscriber telecommunications equipment with particular lines, the central terminal is provided with more knowledge about the subscriber terminals and telecommunications equipment that it supports. The central terminal can use this phone number list to handle calls without utilising fixed timeslot mapping. Hence, assuming the exchange has the ability to include within a call directed to the central terminal information identifying the phone number to which the call is directed, the central terminal will be able to use the phone number list to determine which line should be use for transmitting the call. Thus, irrespective of which time slot the call arrives at the central terminal on, the central terminal can correctly route the call.
This is particularly advantageous when wireless telecommunications systems are used to handle more advanced telephony features such as ISDN (Integrated Services Digital Network), since then the flexibility provided by the system described in UK patent application no 9621070.3 is particularly beneficial. For example, ISDN calls may include phone number information which such a system would be able to use to manage the call without needing to perform any fixed timeslot mapping.
In preferred embodiments of the system described in UK patent application no 9621070.3, the central terminal further comprised a call manager for receiving a call from a subscriber terminal connected to the central terminal, comparison logic for comparing a destination phone number contained within the call with the phone numbers maintained in the phone number list, and routing means, responsive to a match by the comparison logic, to route the call directly to the subscriber terminal to which the telecommunications equipment corresponding to the destination phone number is connected.
Hence, if a call is received at the central terminal from a subscriber terminal which includes information identifying the phone number to which the call is directed, then this phone number information can be compared with the phone numbers in the phone number list held within the central terminal. If the phone number matches one of the numbers in the phone number list, then this indicates that the telecommunications equipment to which the call is directed is connected to another of the subscriber terminals supported by the central terminal. In this instance, it was realised that the call could be routed directly by the central terminal without passing the call via the telephone exchange. This could be useful in a number of situations, for example for exhibition sites, etc where short term local phone facilities may be required. By providing a central terminal and a number of subscriber terminals, a telephone network can be established without wired cables needing to be laid, and the central terminal can then route the calls based on phone number information provided within the calls. A point to multiple point radio link would thereby be provided without the necessity for a connection to the exchange.
However, one drawback that occurs when the central terminal is given the flexibility to route calls internally without reference to the exchange is that the automatic call logging facility that would typically be provided at the exchange to keep a record of calls made through it will no longer be able to keep accurate records of calls to or from subscriber telecommunications equipment of subscriber terminals connected to such a central terminal. Outgoing calls from subscriber telecommunications equipment that are directed by the central terminal through the exchange (eg. because they are not directed to another piece of subscriber telecommunications equipment whose phone number is recorded in the central terminal's phone list) will be logged, whereas those calls routed without using the exchange (eg calls between subscriber telecommunications equipment connected via subscriber terminals to the same central terminal) will not be logged. This is an important issue, since client billing is based on such logs of calls, and statistical data about the telephone network can also be derived from such logs.